Storage Ring Free Electron Laser Dynamics: Longitudinal Detuning Study

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16 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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Storage Ring Free Electron Laser Dynamics:
Longitudinal Detuning Study
Cyrille Thomas
Collaborators:
J.I.M. Botman (TU/e)
G. De Ninno (ELETTRA)
M. E Couprie (LURE)
D. Garzella (LURE)
G. Dattoli (ENEA)
Technische
Eindhoven Universiteit
FEL 2002 -
ANL
I.
Experimental detuning curves
-
Super ACO
-
ELETTRA
II.
Comparison Theory vs. Experiment:
-
Numerical simulations
Detuning curve
:
e-bunch
Laser pulse
δL
e-bunch
RF
Detuning: definition
Delay between the laser pulse and the electron
bunch accumulated in one pass
in the interaction
region
Detuning effect:
νRF
Tlas
= Tb
passage n
Electron bunch
Laser pulse
ν
RF + δνRF
δνRF
> 0
Detuning effect:
Tlas
> Tb
n
n+1
δz
n+2
2 δz
z
Why studying the detuning curves?
Detuning curves characteristics give information about FEL
dynamical system properties
Importance: control the FEL source stability for user applications
Detuning curve
-175
-150
-125
-100
-75
-50
-25
0
25
50
75
100
125
150
175
0
5
10
15
20
25
30
35
40
45
1
2
3
4
5
Super ACO: VhRF
= 0 V, Itot
= 40 mA
I
las
(a.u.)
1Hz ↔
0.36 µm
Delay:
δνRF
(Hz)
Detuning curve
Super ACO: V
hrf
= 150 kV, Itot
= 25 mA
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
-200
-100
0
100
200
δν
(Hz)
RF
2
1
3
4
5
I
las
(a.u.)
Detuning curve
ELETTRA: Itot
= 20 mA
3
2
4
1
5
1
2
I
las
(a.u.)
4
3
-200
δν
(Hz)
RF
0
100
-100
200
Courtesy of ELETTRA FEL group
Laser pulse duration
Super ACO: V
hRF
= 150 kV
δνRF (Hz)
σ
Las
(ps)
-40
-20
0
20
40
60
80
10
15
20
25
30
35
40
45
Pulsed behavior
Super ACO: VhRF = 0 V
ν
(Hz)
Laser
y = 209 -
9.34
δν
y = 130 + 8.85
δν
δνRF
(Hz)
-30
-20
-10
0
10
20
30
40
200
250
300
350
400
450
500
550
ν
Las
(Hz)
Slope depends on
τ
s
Numerical code: integrates differential equations
-
Laser electric field evolution
1-D model coupling:
-
Longitudinal phase space evolution
-
Microwave instability
Numerical detuning curve:
Super ACO
0
100
200
300
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
-100
-200
-300
δν
(Hz)
RF
I
las
/ I
sat
1
2
3
4
5
g0

2 %
|Zn/n| ≈
5 Ω
Itot= 40 mA
Conclusion: width
depends on the gain
Super ACO, detuning curve for two gain values
δν
RF
(Hz)
2.0
1.5
1.0
0.5
0.0
-200
-150
-100
-50
50
100
150
200
0
2.5
I
las
/ I
sat
g0,eff
=1.4 %
g0,eff
=1.3 %
∆ν
= 350 Hz
∆ν
= 200 Hz
Super ACO
2.5
Z = 5.0 Ω
Conclusion: width
reduced by the
Microwave Instability
0
100
-100
0
0.5
1.0
1.5
I
las
/ I
2.0
Z = 5.2 Ω
Z = 6.2 Ω
δν
RF
(Hz)
sat
Numerical detuning curve:
ELETTRA
180
3
160
140
g0

30 %
|Zn/n| ≈
0.5

Itot= 20 mA
120
60
80
100
I
las
/ I
sa
t
4
2
1
5
40
20
0
400
300
200
100
0
100
200
300
400
δνRF
(Hz)
Laser pulse duration
Numerical detuning curve:
Super ACO
-200
-150
-100
-50
50
100
150
200
0
1.6
1.4
1.2
1.0
0.8
0.6
0.2
0.0
0.4
σ
Las
/ σ
b
δν
RF
(Hz)
Close to Fourier limit
g
0
= 2.2 %
* g0,eff
=1.4 %
+ g0,eff
=1.3 %
σb
= 150 ps
Conclusion
:

Detuning measurements done both at Super ACO and ELETTRA

Numerical comparison performed

Qualitative and quantitative agreements found

Detuning curve study:
-
width given by the gain, and reduced by instabilities
-
five zones with characteristic laser behavior: cw and pulsed
-
narrow detuning central zone: laser near Fourier limit